Current research on operant choice (which uses both humans and other animals as subjects) is here related to current research on human decision. The bridge between the two spheres of research is a translation of the concept of probability of outcome (directly experienced or verbally expressed) into operant terms--delay of reinforcement or punishment (as schedules or as discriminative stimuli for schedules). A consequence of this translation is that inconsistencies of choice (as expressed by failure of behavior to confirm to the axioms of probability theory) may be viewed in terms of self control or its lack (where lack of self control, in turn, is a failure to choose a delayed but larger reinforcer over an alcohol and drug abuse, may be seen as failure of self control, the proposed research is directly relevant to mental health.